1.Field of the Invention
This invention relates to pumps and, more particularly, to a novel pump apparatus and method, the pump including a magnetically suspended and rotated impellor.
2. The Prior Art.
Historically, fluids are pumped by a variety of pump apparatus including, for example, positive displacement pumps such as piston-type pumps, moving diaphragm pumps, peristaltic action pumps, and the like. The conventional centrifugal-type pump involves a shaft-mounted impellor immersed in the fluid. The shaft extends through a seal and bearing apparatus to a drive mechanism. However, it is well-documented that shaft seals are notoriously susceptible to wear and also attack by the fluids, resulting in an ultimate leakage problem.
It is also well known that certain special applications require specific pumping techniques. For example, fluids such as corrosive fluids (acids or caustics) and sensitive fluids such as blood, each require specialized pumping techniques.
The pumping of blood involves known hazards. In particular, the shaft seal for an impellor-type blood pump is an area of stagnation and excessive heat. These events foster the formation of thrombus and provide a place for bacterial growth. Seal leakage can also lead to bearing freezing. Numerous attempts to avoid the foregoing problems associated with pumping blood have been made using flexible diaphragm and collapsible tubing in roller pumps. However, the continual flexing of the diaphragm and/or the tubing material is known to (1) change the blood-contacting properties of the material, (2) result in material fatigue with the attendant risk of an eventual rupture, and (3) dislodge fragments of the internal wall of the flexible material causing the fragments to pass as emboli into the bloodstream.
Studies have been made of pumps used as total artificial hearts implanted in experimental animals. These studies have continued for the past 20 years. These pumps can be categorized as producing pulsatile or nonpulsatile flows. Pulsatile pumps universally require valves (mechanical or tissue) with their inherent problems and limitations. While the nonpulsatile pumps generally do not require valve systems, they do require rotating shafts passing through bearings and seals with the inherent problems set forth hereinbefore. Most of these systems (non-pulsatile) have been implanted outside of the body for short-term cardiac assistance and have experienced a moderate degree of success.
Historically, the pump mechanism of these total artificial hearts have been energized with gases (pneumatic systems), electricity (motors, solenoids, etc.), nuckkar energy, and skeletal muscles. The energy sources and their convertor systems possess additional components that increase the complexity of the total systems and thereby contribute to the overall unreliability of the systems. Also, the energy conversion system must be correlated and integrated into the pump design and the total design must be configurated to fit within the available anatomical space. Other drawbacks include (1) high-bulk characteristics, (2) dependence on external pneumatic systems, (3) choice of available materials for fabrication, and (4) multiple bearings and moving parts with inherent limitations in the tested and predicted life expectancies of the same. Most prior art systems inherently have excessively high (1) noise characteristics, (2) vibration, and (3) recoil (thrust) levels.
The current state of the art for blood pumps is being developed in at least four laboratories in the United States. Survival times for calves with total artificial heart replacements of about five months have been experimentally achieved with the longest living about seven months. The natural ventricles of a man have been replaced at least once by a total artificial heart in one reported incident as early as 1969.
One of the inventors has been closely associated with animal experiments involving both total artificial hearts and ventricular assist devices for at least seven years. As a result, he has held most of the survival records obtained with calves having the total artificial heart. These records include at least 38 days for an electromechanical system and 221 days for a pneumatic system. Accordingly, this inventor is very familiar with current research in total artificial hearts and assist devices throughout the world and is thus congnizant of the many problems and limitations with the current state of the art blood pumps. For example, U.S. Pat. No. 3,641,591 involves a flexing diaphragm that limits the material selection and requires a portable energy supply. U.S. Pat. Nos. 3,633,217 and 3,733,616 are electro-magnetically activated and involve flexing diaphragms, mechanical linkages, with a corresponding increased weight and bulk. U.S. Pat. No. 3,896,501 is an electro-mechanical device having a complexity of gears, shafts, and bearings with the attendant problems set forth hereinbefore. Electro-hydraulic systems include U.S. Pat. Nos. 3,048,165; 3,148,624; 3,572,979; 3,636,570; and 3,783,453 and variously involve flexing diaphragms, springs, hydraulic fluid containment tubing and valving in addition to increased bulk and weight.
All of the above, non-pneumatic, blood pumps require a compliance chamber when used in a singular or biventricular assist mode or as a total artificial heart. This compliance chamber must accommodate a volume equal to each stroke volume in the assist device and aid in balancing the differences in right and left ventricular stroke volumes.
U.S. Pat. Nos. 1,061,142; 2,669,668; 3,139,832; 3,411,450; 3,420,184; 3,487,784; 3,608,088; and 3,647,324 all involve electrically powered centrifugal pumps. These pumps each include a rotating shaft, the shaft passing through a seal in the pumping chamber directly from a motor or a magnetic coupler. As set forth hereinbefore, any seal usually constitutes a very hazardous environment while also being subject to failure by leakage into the shaft bearings.
It would, therefore, be a significant advancement in the art to provide a pump characterized by the absence of rotating shafts, seals, bearings, or the like. It would also be an advancement in the art to provide a novel pump apparatus and method whereby the impellor for the pump is magnetically suspended and rotated in the fluid being pumped. It would also be an advancement in the art to provide a novel method for pumping a fluid with a magnetically suspended pump impellor. Another advancement in the art is to provide a novel pump apparatus that is characterized by the absence of valves in the stream flow. It would also be an advancement in the art to provide a pump having a novel valve apparatus in combination with the impellor so that when power is interrupted to the impellor, the valving action automatically closes under reverse flow when the pump is used in the ventricular assist mode. Such a novel pump apparatus and method is disclosed and claimed herein.